Method of making a lined die casting by employing a transplant coating

ABSTRACT

A method for die casting a part having a hard wear resistant liner. The invention is directed to the preservation of the integrity of the liner by initially casting the part with extensions that are machined off during finishing.

United States Patent 1191 Koch [ METHOD OF MAKING A LINED DIE CASTING BY EMPLOYING A TRANSPLANT COATING [75] Inventor: James H. Koch, Oregon, Ohio [73] Assignee: N. L. Industries, Inc., New York,

[22] Filed: Dec. 10, 1973 [21] App]. N0.: 423,065

511 1111. C1. B23p 17/00 [58] Field 6: Search 29/5273, 527.5, 527.6; 164/9, 46, 70, 75, 98, 112, 132

[56] References Cited UNITED STATES PATENTS Bauer 29/527.3 X

1 51 Feb. 11, 1975 3,098,270 7/1963 Bauer 164/132 X 3,216,072 11/1965 Bauer 164/46 3,450,189 6/1969 MaeDonald 164/75 X 3,533,329 10/1970 Galli 29/5276 X 3,797,101 3/1974 Bauer 29/5273 Primary Examiner-C. W. Lanham Assistant Examiner-D. C. Reiiey, 111 Attorney, Agent, or Firm Owen & Owen Co.

57 BSTRACT A method for die casting a part having a hard wear resistant liner. The invention is directed to the preservation of the integrity of the liner by initially casting the part with extensions that are machined off during finishing.

4 Claims, 10 Drawing Figures PATENTED 1 1975 3.864.815

SHEET 1!)? 3 PATENTED FEB] 1 I975 SHEET 2 BF 3 PATENTEI] FEB 1 I I875 SHEET 3 BF 3 METHOD OF MAKING A LINED DIE CASTING BY EMPLOYING A TRANSPLANT COATING BACKGROUND OF THE INVENTION It has been known that it is advantageous to form the housing for a rotary engine of the Wankel type by the die casting process. It has also been known that the interior wall surface of the housing should be of a material of higher melting point than the body of the casting and one which exhibits great resistance to wear and erosion. Typically the body of the housing is cast from an aluminum alloy and the interior coating comprises a layer of metal such as stainless steel, another hard iron alloy, or ceramic material, alloys of refractory metals or hard materials such as tungsten or titanium carbides. The coating is most advantageously applied by the transplant coating process shown and described in Bauer US. Pat. No 3,083,424. The present invention is directed to an improvement of this process for a specialized application.

Many of the coating metals are brittle by nature and since the coating on the longitudinal bore which constitutes the operating face of the housing must be totally continuous and without cracks or chips great care must be exercised in handling the coated core before inserting it into the die casting machine and in handling the casting immediately after the casting operation. If the edges of the coated core become chipped or cracked, and these cracks carry over into the transplant coated surface of the casting then the casting itself must be rejected. The present invention assures that no chipping or cracking of the coating in the operating area of the casting will occur.

At the present time the coating material is sprayed on to each core individually which requires a short cycle including loading of the coating machine, initiation of spraying, stopping and unloading of the spraying machine. The coated core must be then transported to the casting machine although in practice a number of coated cores are held on racks awaiting insertion into the casting die. The present invention provides a method by which a plurality of cores can be loaded and sprayed at the same time, then separated from each other and stored while awaiting introduction into the die casting machine. Further, the invention provides a method whereby the coated surface exposed to the die casting die is so disposed that no cracking or chipping of the active area of the resulting casting can occur. In one modification of the invention each core temporarily has applied to it masking plates which are bolted to opposite faces of the sides of the core prior to spraying. These masking plates stay with the core during both the spraying and casting operations and receive temporary coatings in the same manner as the cores. In another modification of the invention only a single masking 'plate is applied to a core.

BRIEF DESCRIPTION OF THE INVENTION The invention comprises a method of forming by die casting, a coated or composite article, by applying to a core a mask made up of one or more masking plates which as an assembly will ultimately be placed in a die casting machine. The periphery of the assembled mask and core is then sprayed with a material which will form the coating for the interior of the cast article. The coated core and mask as an assembly is then placed in the die cavity of a die casting machine and metal is forced into the cavity under normal die casting pressures. The casting metal bonds securely to the coating material. The casting and core assembly are then removedfrom the die casting machine as a unit. If a single mask has been used, the core and mask can be parted from the casting by differential expansion assuming that the casting is made ofa metal having a relatively higher coefficient of thermal expansion than the core which is usually the case. The core and mask, having a lower coefficient of thermal expansion than the casting, will push easily away axially of the casting. The core assembly is then returned to the spray area for recoating. If two masking plates have been used, one may be removed first from the core assembly and the remaining plate and the core taken from the casting as above described. In either event the transplanted coat will extend well beyond the operating face of the casting since it has been applied to the periphery of the mask which lies outside the operating face of the casting. Thus any small breaks or chips that might occur will appear only as a ragged edge on a bead-like extension around the casting. This extension is machined off during the finishing operations performed on the part and the operating face of the casting exhibits a complete uniformity of coating and structural integrity- BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic elevational view of a group of four cores and associated masks mounted in a coating machine, and undergoing the coating step;

FIG. 2 is a diagrammatic elevational view showing the coated cores separated along an arbor;

FIG. 3 is a diagrammatic view of a coated core mounted in a die after the casting shot has been made, but prior to extraction;

FIG. 4 is an exploded view showing removal of a core and mask from a casting;

FIG. 5 is a diagrammatic view of an alternate form of the invention in which only a single mask is associated with each core during coating;

FIG. 6 is an elevational view of a core and mask assembly;

FIG. 7 is a central vertical sectional view of a casting and core with anassociated mask coated in accordance with the procedure indicated in FIG. 5;

FIG. 8 is an exploded view of a casting, core and mask after extraction and disassembly in which the core is coated in accordance with the procedure of FIG. 5;

FIG. 9 is a fragmentary enlarged view of the area shown in the circle in FIG. 4; and

FIG. 10 is an enlarged sectional view of the area shown in the circle in FIG. 8.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT A preferred embodiment of the method of the present invention will be described with reference to the dual mask structure shown in FIGS. 1, 2, 3, 4 and 9. As there indicated, each of a plurality of core pieces 11 is mounted on the arbor or spindle 12 of a rotating machine that resembles a lathe having a headstock l3 and some means for driving the same (not shown). Each of the cores 11 is flanked by a masking plate 14 on each side. The masking plates follow the contour of the cores but are made slightly larger than the cores for reasons which will be subsequently described. Each of the masking plates 14 is chamfered at its periphery so that when two masking plates abut each other a V- groove is established at to facilitate cracking the coated assembly apart into discrete coated core-plate elements. The masking plates 14 may be bolted to or held in association with the cores 1! in any suitable.

manner.

Once mounted on the arbor 12 of the coating machine, the entire assembly is sprayed with the material that will ultimately form the transplant coat as shown and described in Bauer US. Pat. No. 3,083,424. The coating gun is diagrammatically indicated at 16 in FIG. 1. The gun is moved laterally during the coating process as diagrammatically shown from a position in which the innermost core assembly is sprayed to a position in which the outermost core assembly is sprayed, the coating being equally deposited throughout the length and periphery of the cores and plates.

When the cores have been sprayed as indicated in FIG. 1 they are separated from each other by driving a wedge element 17 between the plates 14 into the chamfer or V-groove 15 (see FIG. 2). This cracks the coating apart in the region of the groove 15 and permits each of the coated cores with its assembled masking plates 14 to be stored as a separate element prior to casting.

As shown in FIG. 3 the coated core and plate assembly is inserted in the die of a die casting machine and the shot is made in a normal manner. As shown in FIG. 3 the metal of the casting enters intimately against the coated core and also against the periphery of each of the coated masking plates 14. In casting the part it is advantageous to gate the die at the center to reduce the path taken by the molten metal, although conventional side gating has been used with satisfactory results.

Subsequent to the casting operation the casting, core and plates are removed from the machine as a unit. As indicated in FIG. 4 one of the masking plates is released from engagement with the core and removed outwardly simply by driving it away while the core 11 and the other of the masking plates 14 are removed as a unit from the completed casting. This latter removal is preferably made by differential expansion. If the casting and core assembly are heated, the casting will expand to a greater extent than the core since the casting is made of aluminum alloy or other light metal and the core is usually an iron alloy having significantly lower coefficient of thermal expansion. This differential expansion permits the easy removal of the now coated casting from the core and the coating is said to be transplanted from the core to the interior longitudinal bore of the casting.

As indicated in FIG. 9 the casting has a bead-like peripheral extension which has received the coating from the masking plate 14 on each side. It is necessary to machine the casting to form a precisely finished active side face by which the housings of a two-rotor engine are abutted with an interposed gasket and against which the end plates of the engine will lie in service. When the active face of the housing is machined away the beads 20 are also machined away and no coating appears on the sidewalls of the finished housing. The coating is confined to the inner surface of the housing.

A second modification of the method of the present invention is indicated diagrammatically in FIGS. 5, 6, 7, 8 and 10. In this form of the method only a single masking plate is used between each of the core ele- 4 ments 10. The masking plates are designated 14a in FIG. 5. The masking plates are fixed to one side of each of the cores and the other side of each of the cores is slightly grooved as at 21. In this method a spray gun 22 v directs the spray of coating material particles at an angle to the axis of the cores as shown in FIG. 5. As there indicated, a spray angle of approximately 45 degrees would be satisfactory, and the spray gun 22 is moved axially over the assembled group of cores. Since the masking plates, designated 14a are larger in diameter than the associated cores they exert a shielding effect on that portion of each of the cores in their shadow". The sprayed material is deposited with a heavy deposit ,on one side of the masking plate and a substantially lighter, practically non-existent, coating on the opposite-side of the masking plate in that region 21 where the core is grooved.

Once the group of cores has been sprayed separation of the same is relatively easy because of the absence of the binding coating material at the point where separa-' tion occurs. The coated core and assembled masking plate are inserted into the die of a die casting machine and the casting is made. The core is then disassembled from the casting as shown in FIG. 8 and the masking plate 14a may be removed from the cores if desired or may be left in place.

As indicated in FIG. 10 the casting has a circumferential bead to which the coating is transplanted on that side where the masking plate 14a occurred. On the opposite side the casting has abead that extends radially inward relative to the coated surface where the grooved portion of the core occurred. This inwardly extending bead has almost no coating on it. In finishing the casting both of the side beads are machined away leaving an active side face that may be precisely finished as in the previous modification of the invention. The coating on the interior longitudinal bore surface of the casting is thus protected in each instance from cracking or chipping in those areas where a wear resistant surface is necessary.

Various other modifications of the invention will be apparent to those skilled in the art, and such modifications may be made without departing from the scope of the appended claims.

What I claim is:

1. A method of forming a die casting having an interior longitudinal bore surface which is coated with a hard wear resistant material and side faces which are initially formed with bead portions that are machined off in the finishing of the completed casting, which method comprises assembling on an arbor a group of die cores and interposed masking plates between the cores, spraying the coating material over the exposed peripheral surfaces of the cores and masking plates, individually separating the core assemblies from each other so that each core remains attached to at least one masking plate and the coating thereon remain undisturbed, introducing the coated core and attached masking plate into a die, introducing molten metal into the die under normal die casting pressures to adhere to the coating material, removing the completed casting and core and masking plate from the die as a unit, separating the core and masking plate from the casting leaving a coated longitudinal bore and a coated extending bead portion in that area where the masking plate occurred, and machining away the extending bead and its 6 gle masking plate is affixed to the opposite side of the core, and in which spraying of the coating is directed at an acute angle against the assembled cores and plates in a direction such that the plates shield the grooved core area against the deposition of coating material. 

1. A method of forming a die casting having an interior longitudinal bore surface which is coated with a hard wear resistant material and side faces which are initially formed with bead portions that are machined off in the finishing of the completed casting, which method comprises assembling on an arbor a group of die cores and interposed masking plates between the cores, spraying the coating material over the exposed peripheral surfaces of the cores and masking plates, individually separating the core assemblies from each other so that each core remains attached to at least one masking plate and the coating thereon remain undisturbed, introducing the coated core and attached masking plate into a die, introducing molten metal into the die under normal die casting pressures to adhere to the coating material, removing the completed casting and core and masking plate from the die as a unit, separating the core and masking plate from the casting leaving a coated longitudinal bore and a coated extending bead portion in that area where the masking plate occurred, and machining away the extending bead and its coating material to leave a smooth active side face of the die casting.
 2. A method as claimed in claim 1 in which a masking plate is affixed to each side of each core.
 3. A method as claimed in claim 1 in which a masking plate is affixed to only one side of a core.
 4. A method as claimed in claim 1 in which the core piece is grooved inwardly adjacent one edge and a single masking plate is affixed to the opposite side of the core, and in which spraying of the coating is directed at an acute angle against the assembled cores and plates in a direction such that the plates shield the grooved core area against the deposition of coating material. 